The inventive subject matter relates to power conversion apparatus and methods and, more particularly, to uninterruptible power supply (UPS) apparatus and methods.
UPS systems are commonly used in installations such as data centers, medical centers and industrial facilities. UPS systems may be used in such installations to provide backup power to maintain operation in event of failure of the primary utility supply. UPS systems may have a modular structure including two or more UPS modules, each of which may include, for example, a rectifier, an inverter and a DC/DC converter for interfacing to a battery or other DC power source. The modules commonly are designed to operate in parallel to provide scalable power capacity, e.g., the modules may be coupled in common to an AC source, a DC source (e.g., a battery) and/or a load. An example of such a modular UPS system is the Eaton Power Xpert 9395 UPS system, which may be configured to include two or more uninterruptible power modules (UPMs), each of which include a double conversion UPS circuit including a rectifier, inverter and battery converter coupled to a common DC bus.
Large data centers have proliferated with the advent of web services and cloud computing. Some newer large data centers occupy millions of square feet and house hundreds of thousands of servers. Typically powered by the local grid, these centers may include backup power supply systems including UPSs and diesel-electric backup generators to support continued operation when utility power is lost. Energy consumption is a major concern for such facilities, as some facilities are approaching the 100 MW level. For such facilities, even a few percentage points of efficiency can translate into significant expense.
Techniques for improving UPS efficiency have been developed. For example, some double-conversion UPS systems support high-efficiency or “eco” modes in which the rectifier and inverter are bypassed when the input AC source meets certain criteria. Other solutions to increase data center energy efficiency, such as those described, for example, in U.S. Pat. No. 7,886,173 to Krieger et al., U.S. Pat. No. 7,560,831 to Whitted et al. and U.S. Pat. No. 8,344,546 to Sarti, include redundant power distribution techniques that avoid the use of traditional UPS architectures.